The present invention relates generally to a fail-safe device in an electronic control system for an automotive vehicle. More particularly, the invention relates to a fail-safe device having a means for outputting output control data to a vehicle controlling device which is part of a vehicle electronic control system. The means is connected with an output unit of the control system so that the output therefrom can be used for engine control to replace the output of a central processing unit (CPU) when the central processing unit fails to operate.
Recently, electronic control systems using a microcomputer have been employed in automotive vehicles for controlling various vehicle devices. For example, it is popular to use the electronic control system in an engine control system for controlling engine revolution speed, fuel amount to be fed into the combustion chamber of the engine, spark ignition timing and so on. In such electronic control systems, the CPU operates to output a control output to be fed to the vehicle device to be controlled. The vehicle device which is part of the electronic control system is inoperative unless the CPU is operating correctly. Therefore, the vehicle devices may stop operation when the CPU fails to operate.
For example, in the case in which the vehicle device incorporated within the electronic control system is the internal combustion engine, failure of CPU operation may possibly cause the engine to stop operation and thus stop the vehicle.
Therefore, a fail-safe device for the electronic control system for the automotive vehicle is necessary, so that the fail-safe device can replace the CPU operation for maintaining the controlled vehicle device in an operative state even when the CPU fails.